Balancing paging load and tracking area updates

ABSTRACT

A method for assigning a tracking area (TA) is disclosed. A mobility state of a wireless transmit/receive unit (WTRU) is determined and the TA is assigned based on the determined mobility state. Also disclosed is a method for accessing a closed subscriber group (CSG) TA. A CSG TA identifier is received at a WTRU and is stored. A CSG TA broadcast is received and the broadcast CSG TA is accessed if an identifier of the broadcast CSG TA matches the stored CSG TA identifier. Also disclosed is a method for changing a mobility state of a WTRU. A current mobility state of the WTRU is determined and a predetermined metric of the WTRU is examined. The predetermined metric is evaluated to determine if the metric has crossed a threshold and the mobility state is changed based on the evaluated metric.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/925,116 filed Jun. 24, 2013, which is a continuation of U.S. patentapplication Ser. No. 12/044,491 filed Mar. 7, 2008, which issued as U.S.Pat. No. 8,472,956 on Jun. 25, 2013, which claims the benefit of U.S.Provisional Application No. 60/893,640, filed Mar. 8, 2007, the contentsof which are hereby incorporated by reference herein.

FIELD OF INVENTION

The present invention is related to wireless communications.

BACKGROUND

The third generation partnership project (3GPP) has lately initiated theLong Term Evolution (LTE) program to bring new technology, new networkarchitecture, new configuration, and new applications and services tothe wireless cellular network in order to provide improved spectralefficiency and faster user experiences.

In LTE, the tracking area (TA) concept replaces the universal mobiletelecommunications system (UMTS) routing area/location area (RA/LA) andUMTS terrestrial radio access network registration area (URA) conceptsto simplify the mobile area tracking operations and to reduce theoverhead caused by the area updates a wireless transmit/receive unit(WTRU) has to perform. When a WTRU is in the LTE_IDLE state, it istypically not transmitting or receiving any packets. Because the WTRU isnot in active communication with a base station or an enhanced Node B(eNB), its location may not be exactly known. A TA represents an area inwhich the WTRU was last registered, and it is necessary to page the WTRUin the TA to locate the WTRU in a particular cell. A TA update (TAU) isgenerated when the WTRU crosses the boundary from one TA to another TA.

In WTRU idle mode, the TA concept also includes RA updates (RAU) and LAupdates (LAU) or combined RAU/LAU. The current LTE system has definedtwo TA operational schemes: the “multiple-TA registration” scheme andthe “overlapping TA” scheme.

In the “multiple-TA” scheme, an LTE cell belongs to only one TA, but aWTRU can be assigned with more than one TA. If one WTRU is assigned tomultiple TAs, the WTRU does not need to perform TAUs when it crosses theboundaries between assigned TAs.

In the “overlapping TA” scheme, one cell can be assigned to multiple TAs(broadcast in system information) and one WTRU is assigned only to oneTA. In the overlapped cell, the WTRU does not have to perform a TAU ifits assigned TA is in the TA list of the overlapped cell.

Consideration has been given to allocating TAs to reduce the number ofTAUs and the consequent signaling overhead to the system. Thearrangement and assignment of TAs in the LTE network affects the idlemode paging operation because the WTRU paging is performed by cells inall the assigned TAs. Additionally, in the multiple-TA list scheme, aWTRU may be allocated more than one TA. In the LTE_IDLE state, thenetwork is aware of the WTRU only at a TA level. This means that, forpaging and other purposes, the network can only contact the WTRU overall assigned TAs, which may unnecessarily increase the paging load.Further, the criteria and methods used in allocating multiple TAs to aWTRU are unclear.

Recently, there has also been considerable interest regarding“femto-cells”. These are cells of a short-range base station that may bedeployed in a home or in certain public places (e.g., underground malls,train stations, etc.) to provide cellular coverage in areas that may notbe accessible to macro-cells or to provide differentiated charging tousers when they are accessing these cells. Such cells are referred to asfemto-cells, Home Node B (HNB) cells, Home e-Node B (HeNB) cells or,most commonly, Closed Subscriber Group (CSG) cells.

It would therefore be beneficial to provide a method and apparatus thatcan provide the network with mobility and positioning information toassist in allocating TAs and also help achieve the best possible balancefor the LTE system load between the operations of system paging and theTAUs.

SUMMARY

A method and apparatus for LTE tracking area (TA) operations with theaim of achieving a balanced system paging load and reducing the numberof unnecessary tracking area update (TAU) requests are disclosed. TheLTE TA operational mobility states, their transitions on the WTRU, andtheir signaling to the network so that the proper balance can beachieved between the LTE TAU requests and LTE paging operations are alsodescribed. Various mechanisms are provided for addressing these issues,including WTRU mobility detection from WTRU positioning measurementresults, WTRU cell reselection numbers and the TAU counts, and by theuse of adjustable TA timers.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example and to be understood in conjunction with theaccompanying drawings, wherein:

FIG. 1 shows a TA deployment for a multiple TA list scheme;

FIG. 2 shows a TA deployment for an overlapping TA scheme;

FIG. 3 is a mobility state transition diagram for a wirelesstransmit/receive unit (WTRU);

FIG. 4 is a flowchart of a method for transitioning a WTRU from a lowmobility state to a high mobility state;

FIG. 5 is a flowchart of a method for transitioning a WTRU from a highmobility state to a low mobility state;

FIG. 6 is a block diagram of a WTRU configured to perform TAUs and cellreselections; and

FIG. 7 is an exemplary signal diagram of TA operations.

DETAILED DESCRIPTION

When referred to hereafter, the term “wireless transmit/receive unit(WTRU)” includes, but is not limited to, a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the term “base station” includes but is notlimited to, a Node B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

TA Allocation

At the system level, the following TA allocation principles are usedwith respect to each of the current TA allocation schemes.

1. When the WTRU is mobile, it should perform as few TAUs as possible toreduce the system signaling load. This means that the TA or TAs shouldcover as many cells as possible, so that a WTRU reselecting from cell tocell does not trigger a TA update.

2. When the WTRU is relatively stationary, the LTE paging caused by anincoming call to the WTRU should be conducted in as few cells aspossible to reduce the paging load system-wide.

To achieve the proper balance of the TA allocation principles, thefollowing TA allocation schemes can be utilized.

1. Multiple TA list scheme. When the WTRU is in the stationary state orin the low mobility state, only one TA is assigned to the WTRU. Withonly one TA, the WTRU will not incur many TAUs, but the system can pagethe WTRU in a small scope area in one TA. When the WTRU is in the highmobility state, multiple TAs can be assigned to the WTRU to minimize thenumber of TAUs. However, each cell belongs to only one TA.

FIG. 1 shows a TA deployment for a multiple TA list scheme. Inparticular, FIG. 1 shows the deployment and composition of differentTAs, i.e., large TAs and small TAs. A large TA usually coversgeographical areas with many cells where the WTRUs generally move fastover a sustained period; for example, in a highway area. In this orsimilar areas, the TA can be laid over many LTE cells along the movingpath. This is shown by the large TA-3 and TA-4 and their associatedcells.

Small TAs are generally deployed to places where WTRUs are in lowmobility or even stationary, such as small TA-1 and small TA-2. SmallTAs can also be deployed adjacent to the high speed areas. Specificcells, such as Cell-1 and Cell-2 in FIG. 1, are located near theentrance to the highway and therefore WTRUs will be assigned to multipleTAs (TA-3 and TA-4) for the high-speed movement with few TAUs.

2. TA overlapping scheme. An individual cell may belong to more than oneTA. A two-level TA coverage scheme is employed such that when the WTRUis in a high mobility state, the WTRU is assigned to a TA that covers alarge geographical area with many individual LTE cells. With the largerTA, the WTRU does not have to perform many TAUs. When a WTRU is in thelow mobility or stationary state, it is assigned to a TA that has asmaller geographical area with a fewer number of cells. The transitionbetween a large TA and a small TA may happen in a cell covered by bothTAs.

FIG. 2 shows a TA deployment for an overlapping TA scheme. Inparticular, a large TA is generally assigned to cover the geographicalareas where the WTRU is able to move fast in a sustaining period, forexample in the highway area, while small TAs are assigned to the cellswhere WTRUs are not moving fast. The overlapping cells (for example,Overlapping-Cell-1 and Overlapping-Cell-2 in FIG. 2) situated in both alarge TA and a small TA are usually deployed for the small TA (such asin a mall area adjacent to the highway), where many stationary or lowmobility WTRUs are camped.

CSG Cell TA

A CSG cell is a very small cell that is usually intended to cover onehousehold worth (for example) of territory. A CSG TA thus represents theTA of one or more small CSG cells covering the small area over whichcellular coverage is desired (e.g., a home or underground shoppingmall). The only WTRUs that are allowed access to the CSG cells are thoseWTRUs whose Universal Subscriber Identity Module (USIM or its LTEequivalent or another application residing in the Universal IntegratedCircuit Card (UICC) of the WTRU) includes the CSG TA ID(s) of the CSGcell(s).

The CSG TA ID may be similar in structure to a macro-cell TA ID in thatthe CSG TA ID may be determined be concatenating a CSG TA Code (TAC) andthe operator's Public Land Mobile Network (PLMN) ID. The CSG TAC may bethe same length as the macro-cell TAC. Alternatively, the CSG TA ID mayhave a different format, structure, or length than a macro-cell TA ID.The WTRU in its USIM (or in any other application residing in the UICC)may store only a part of the CSG TA ID.

The CSG TA ID may have an indicator field to indicate the CSG cellproperty/scale. The CSG cell may broadcast the CSG TAC and the PLMN IDin separate fields and the WTRU (e.g., in the NAS layer) may have toconstruct the CSG TA ID from the broadcast information. The WTRUs withthe CSG cell's TA ID in their USIM allowed TA list may belong to aclosed subscriber group for the CSG Cell or the HNB.

When a WTRU in Idle Mode detects a CSG cell having a TA ID that is notconfigured in its USIM (or its LTE equivalent or in another applicationresiding in the UICC), it will not attempt to access that CSG cell andwill not perform a TAU procedure. It is proposed that the non-accessstratum (NAS) Tracking Area Accept message include new InformationElement(s) (IE) which allows the network to configure the WTRU with theTA IDs of the CSG cells that the WTRU has access to. In oneimplementation, the IE includes the TA ID(s) of the CSG cell(s) that theWTRU has access to.

If a WTRU in Idle Mode detects a CSG cell that has a TA ID which isincluded in its list of allowed CSG cell TA IDs, but is not included inits allowed list of TA IDs (for signaling free mobility), it mayconclude that it has access to this CSG cell but a TAU procedure needsto be triggered upon Idle Mode cell selection/re-selection to this CSGcell. In other words, signaling free mobility (i.e., mobility betweentwo cells belonging to different TAs without performing a TAU procedure)between a macro TA and CSG TA may be permitted only when the CSG TA IDis included explicitly as one of the multiple TAs configured for theWTRU by the network for signaling free mobility (e.g., in the multipleTAs configured in the TAU procedure).

A CSG cell or macro cell may indicate (e.g., using the SIBs on thebroadcast channel) whether signaling free mobility is permitted or not.Such an indication may be provided, for example, by a one bit indicator.If a suitable indication is present, the WTRU may camp on the CSG cellwithout performing a TAU procedure, provided that the CSG TA ID isconfigured in the WTRU. Alternatively, a WTRU may always camp on a CSGcell without performing a TAU procedure provided that the CSG TA ID isconfigured in the WTRU. In the absence of such an indication or if theindication is negative, the WTRU may camp on the CSG cell, but willperform a TAU procedure provided that the CSG TA ID is configured in theWTRU.

In order for WTRUs outside the CSG cell TA user group (referred to as“visitor WTRUs”) to access the CSG cell TA, they may need to execute aspecial code (e.g., 511) or a procedure through the operator. An exampleof a procedure is the “two-factor authentication” procedure with atimely generated authentication code from the host access point(AP)/enhanced Node B (eNB) to acquire a temporary time-limited access tothe CSG cell TA (thus the CSG cell AP allows certain special accesscodes). On successful temporary registration, only this one TA isassigned. Involved multiple TAs may also be assigned if a frequent TAUping-pong effect is observed. The ping-pong effect in thesecircumstances occurs when the WTRU sends unnecessary TAUs when it isaccessing a CSG cell.

All WTRUs in the CSG cell TA are considered stationary or low mobility.Accordingly, no periodic TAU or a long periodic TAU is proposed if theWTRUs are in the LTE_IDLE state. Paging to the allowed WTRUs in this TAcan thus be directed to this one small cell or to only the assigned TAs,where the TAU ping-pong effect has often been observed.

Mechanisms for WTRU Mobility Detection

There are a number of mechanisms for WTRU mobility detection. The TAUcounting, cell reselection counting, and positioning detection arecoordinated efforts between a WTRU and the network. The WTRU performsthe actions, such as detecting the change (e.g., TA change, cellcoverage change, and position change) and signals the updates (TA orcell) or reports the position to the network. The network collects thestatistics and determines the mobility state of a WTRU and assigns theTA(s) accordingly.

1. Number of TAUs. When the WTRU is transitioning from the low mobilitystate to the high mobility state, counting the number of TAUs can beused as the threshold to trigger the change. LTE WTRUs in the lowmobility state are usually under the TAs with small or medium sizes, andwhen the WTRUs accelerate to a higher speed, the need to have a large TAmay be measured via TAU counting. A number of TAUs (x) on different TAswithin a fixed time (y) may be used as a mobility state triggercriterion.

2. Number of cell reselection decisions. When a WTRU in the highmobility state is reducing its speed (such as exiting from a highway),one measurement of the reduced mobility in the LTE_IDLE state is thenumber of cell reselections made by the WTRU. The LTE WTRUs cannot usethe TAU counting in the high mobility state, since they are usuallyalready assigned to large TAs to reduce the number of TAUs; therefore,the TAU count would not be an accurate mobility measure.

It should be noted that the cell reselection counting can also be usedfor determining whether the WTRU is transitioning from a low mobilitystate to a high mobility state.

3. WTRU positioning assisted mobility detection. Given that the LTEWTRUs will mostly have the positioning device support, the WTRU'smobility state can be measured with the positioning measurement results,i.e., the positioning longitudes and latitudes. The absolute positioningoffsets obtained by the LTE WTRUs provide the network with the WTRUspeed, which when combined with the TAU counting or the cell reselectioncounting is an accurate measure with respect to the mobility statedetection.

4. WTRU mobility detection based on WTRU Doppler measurement. A WTRU maynot have GPS capability, so the Doppler measurement by the WTRU can beused to detect the WTRU speed. This method can be combined withabove-mentioned counting methods to obtain the WTRU mobility stateinformation.

WTRU Mobility States and Mobility State Transitions

FIG. 3 is a mobility state transition diagram for a WTRU. The LTE WTRUsmay be in a number of mobility states, including, but not limited to:stationary state, low mobility state, and high mobility state.

LTE WTRUs in the stationary state are stationary in the LTE_IDLE statewhen they are not moving or hardly moving in terms of crossing cellboundaries via cell reselections. As a result, these WTRUs rarelyperform TAUs (except the periodic TAU regulated by a TAU timer).Therefore, these stationary LTE WTRUs can be assigned to a single smallTA with one or a few cells to reduce the system paging load.

In the low mobility state, LTE WTRUs are moving or changing locationswith low speed (e.g., reselecting new cells x times over a period of yseconds, or moving under z kmph), such as driving slowly in localstreets or on congested highways. WTRUs in the low mobility state can beassigned to one or a few TAs (multiple TAs) or cells with overlappingTAs, where the TAs are small (i.e., one TA covers a number of cells)that the LTE_IDLE state WTRU's TAU load and the incoming call pagingload are balanced.

In the high mobility state, LTE WTRUs are moving fast, such as drivingalong a highway and changing cells rapidly (exceeding x times per yseconds). LTE WTRUs in this state can be assigned to many TAs (multipleTAs) along the fast mobile path or to a large TA which covers many cellsand many smaller TAs (overlapping TAs). When a WTRU is in the highmobility state, reducing the number of TAUs is an importantconsideration.

FIG. 4 is a flowchart of a method 400 for transitioning a WTRU from alow mobility state to a high mobility state. The method 400 begins withthe WTRU in a low mobility state (step 402). The WTRU performs a TAU ora cell reselection (step 404) and counts the number of TAUs or thenumber of cell reselections (step 406). A determination is made whetherthe number of TAUs or the number of cell reselections is greater than apredetermined threshold (step 408). If the number of TAUs or the numberof cell reselections is below the threshold, then the method continuesperforming TAUs or cell reselections (step 404). If the number of TAUsor the number of cell reselections exceeds the threshold (step 408),then the WTRU transitions to a high mobility state (step 410) and themethod terminates (step 412).

FIG. 5 is a flowchart of a method 500 for transitioning a WTRU from ahigh mobility state to a low mobility state. The method 500 begins withthe WTRU in a high mobility state (step 502). The WTRU performs a cellreselection (step 504) and counts the number of cell reselections (step506). A determination is made whether the number of cell reselections issmaller than a predetermined threshold (step 508). When a WTRU is movingslower, it will be performing fewer cell reselections. If the number ofcell reselections is greater than the threshold, then the methodcontinues performing cell reselections (step 504). If the number of cellreselections is less than the threshold (step 508), then the WTRUtransitions to a low mobility state (step 510) and the method terminates(step 512).

FIG. 6 is a block diagram of a WTRU 600 configured to perform TAUs andcell reselections and a network/eNB 620 to perform the mobility statedetermination function. The WTRU 600 includes a transmitter/receiver 602and an antenna 604 connected to the transmitter/receiver 602. A TAUfunction 610, a cell reselection function 612, and a WTRU positioningfunction 614 are configured to perform TAUs, cell reselections, and WTRUposition detections, respectively, and are in communication with thetransmitter/receiver 602 via a reporting function 618. The WTRU alsomaintains a mobility state function 616 for its Idle Mode mobilitymanagement.

The network/eNB 620 includes a transmitter/receiver 622 and an antenna624 connected to the transmitter/receiver 622. A TAU/cell reselectioncounter and WTRU position monitor function 626 is in communication withthe transmitter/receiver 622 and is configured to count TAUs and/or cellreselections and to receive updates of the WTRU's current position. Amobility state determination function 628 is configured to maintain themobility state of the WTRU 600 and is in communication with the counter626 and the transmitter/receiver 622. The network/eNB 620 can performboth the method 400 and the method 500.

TA Timer Management

In most cases, when the WTRU is in the LTE_Active state, the networkwould have known the location of the WTRU through the cell updateprocedure which the WTRU must have performed. Hence, periodicallyupdating the TA (via a timer) might not be necessary, unless the networkwishes to do so. This could be done either explicitly or implicitly.Alternatively, the network could signal the timer and instruct the WTRUto start the timer when it transitions to the LTE_IDLE state.

In the LTE_IDLE state, it might be necessary for the network to haveaccurate TA level information of the WTRU to minimize the paging load.The WTRU could be in different mobility scenarios: stationary, lowmobility, and high mobility. The network could allocate a single timerwhose length is appropriate given the mobility state of the WTRU.Alternatively, the network may allocate multiple timers (e.g., one foreach mobility state or one for each assigned TA) with their lengthsadjusted so as to achieve optimum paging efficiency versus TAUefficiency and the WTRU may have the ability to start and re-start thesetimers given its estimate of its mobility state and/or current TA.

Scale of a TA

The network may choose to indicate to the WTRU, as part of itsprocedures, the relative size of each TA. In case of multiple TA lists,it may choose to do so using a TAU response. In general, the network mayput this information on the SIB of a broadcast channel from a cell.Alternatively, the TA ID may reserve an indication field for the scopeof the TA area, to facilitate the WTRU making the desired cellreselection decision at the TA boundaries based on its mobility state(from the mobility state function 616) and subsequently requesting theTAU with the choice of TA based on its mobility state (from the mobilitystate function 616).

Balancing TAU and Paging Traffic

From the system point of view, the WTRU TA assignment for balanced TAUand paging load by the network is accomplished with the help of theWTRU's mobility state information. FIG. 7 is an exemplary signal diagram700 of TA operations between a WTRU 702 and a network 704.

When the WTRU 702 is turned on, it sends out an ATTACH Request message710 or the LTE equivalent message to register with the network 704. TheATTACH Request message 710 includes the WTRU ID (Packet-Temporary MobileSubscriber Identity (P-TMSI) or International Mobile Subscriber Identity(IMSI)) and the old TA ID last assigned before the WTRU 702 detachedfrom the network 704. Optionally, the WTRU 702 can also send the“WTRU-mobility-info” information element (IE) with available informationto help the network 704 assign TAs for the WTRU 702.

The network 704 accepts the registration request from the WTRU 702 andsends an ATTACH Accept message 712 to the WTRU 702. The message 712includes the newly assigned TMSI and the new TA ID(s) for the TA thatthe WTRU 702 is assigned to, possibly based on the mobility information.

When the WTRU 702 performs a TAU, the WTRU can send a TA Request message714, which includes the WTRU mobility information (such as the locationchange information, the cell reselection count, or the derived WTRUmobility state information) to the network 704 on the assignment to theTAs. The WTRU mobility information can also include the WTRU's mobilitystate, the number of cell reselections, WTRU position change measurementresults, and the preferred TA-ID.

The network 704 responds to the TA Request message 714 by sending a TAUAccept message 716, which assigns new TAs with corresponding TA ID(s),TMSI(s), and TA timers, based on the WTRU mobility information containedin the TA Request message 714.

Although the features and elements are described in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU)comprising: circuitry configured to: receive a list of closed subscribergroup (CSG) cell identities that the WTRU is permitted to access; campon a CSG cell whose identity is not in the list; and on a condition thatthe WTRU is camping on a CSG cell whose identity is not on the list, toinitiate a tracking area update procedure.
 2. The WTRU of claim 1,wherein the WTRU is assigned to a plurality of Long Term Evolution (LTE)tracking areas.
 3. The WTRU of claim 2, wherein the plurality of LTEtracking areas are used at the edges of at least one of the plurality ofLTE tracking areas.
 4. The WTRU of claim 1, wherein the circuitry isfurther configured to transmit an indication that the WTRU has selecteda CSG cell whose identity is not on the list.
 5. The WTRU of claim 1,wherein the circuitry is further configured to periodically update atracking area of the WTRU.
 6. The WTRU of claim 5, wherein the circuitryis further configured to periodically update the tracking area inresponse to an expiration of a timer.
 7. The WTRU of claim 1, whereinthe circuitry is further configured to transmit mobility information. 8.The WTRU of claim 1, wherein the circuitry is further configured to senda tracking area update request.
 9. The WTRU of claim 1, wherein thecircuitry is further configured to exchange non-access stratum (NAS)signaling.
 10. The WTRU of claim 1, wherein the circuitry is furtherconfigured to initiate the tracking area update procedure to balance asignaling load.
 11. A method performed by a wireless transmit/receiveunit (WTRU), the method comprising: receiving a list of closedsubscriber group (CSG) cell identities that the WTRU is permitted toaccess; camping on a CSG cell whose identity is not in the list; and ona condition that the WTRU is camping on a CSG cell whose identity is noton the list, initiating a tracking area update procedure.
 12. The methodof claim 11, wherein the WTRU is assigned to a plurality of Long TermEvolution (LTE) tracking areas.
 13. The method of claim 12, wherein theplurality of LTE tracking areas are used at the edges of at least one ofthe plurality of LTE tracking areas.
 14. The method of claim 11, furthercomprising transmitting an indication that the WTRU has selected a CSGcell whose identity is not on the list.
 15. The method of claim 11,further comprising periodically updating a tracking area of the WTRU.16. The method of claim 15, wherein the periodically updating thetracking area further comprises periodically updating the tracking areain response to an expiration of a timer.
 17. The method of claim 11,further comprising transmitting mobility information.
 18. The method ofclaim 11, further comprising sending a tracking area update request. 19.The method of claim 11, further comprising exchanging non-access stratum(NAS) signaling.
 20. The method of claim 11, further comprisinginitiating the tracking area update procedure to balance a signalingload.